: 1970 deville rear axle and drive shaft

12-13-10, 05:11 PM
Im looking to upgrade my driveshaft but am unsure of a few things:
Is this a 3.5" diameter shaft? If not then what dimension?
And what axle did this come with, if it varies how can I find out?
Thank you very much

Im looking to upgrade the driveshaft now and replace the rear axle with a 12 bolt gm eventually so I was hoping it would fit within both.
Thanks again!

12-13-10, 05:15 PM
The rear in your Cadillac is already as strong as a 12 bolt. No need to change it. No idea of the diameter of your shaft, but if you are looking to upgrade, call Denny's.

12-13-10, 05:34 PM
What motor/tranny combo do you plan on using?

12-13-10, 06:09 PM
It funny... I was just talking to a guy trying to find a drive shaft for a '71; said they cost $500-$1,000.

12-13-10, 06:42 PM
No idea of the diameter of your shaft, but if you are looking to upgrade, call Denny's.

that's what she said... :yup:

12-13-10, 06:46 PM
^I don't think that work out the same way as you intended...

12-14-10, 07:14 AM
What motor/tranny combo do you plan on using?

Its a twin turbo oldsmobile 455 with a turbo 400, about 650 horsepower. and Dennys was the place I asked! Is it really pretty close to those eaton rear axles with a posi that go for about 2k-3k?? So maybe its worth rebuilding with a posi instead?

12-14-10, 08:15 PM
I dunno if you're looked things over very closely, but here's my humble opinion:
You are asking for a LOT of work that you have not foreseen. The Cadillac rear end has a very special build to allow the driveshaft to ride very low in the car. Too, the tunnel is very low in the car. The engine also has a bit more rake to achieve the same end.

Now, if you simply swap in a 12 bolt, you will lose:
The rear CV joint, as it is a flange-mount.
The special low entry of the pinion.
This will cause:
You will now need a custom driveshaft, as you can no longer utilise the CV joints. You will then need to raise the shaft in the car to keep the U-joints in phase and in line.
You will also need to raise the driveshaft tunnel, for the above reasons. This will affect the entire interior, as the seats are not designed for a high tunnel, which you now need.
Not to mention that most 12 bolt rears do not come with enough brake for this car, so you'll need truck brakes.


12-15-10, 03:34 AM
Ok thank you very much! If I were to get Danny's driveshaft for the stock rear axle what type of axle do I tell him? And are there any specifications out there (ex. drive shaft length & diameter) so that when I order it, that it will bolt right up? And what type of pinion yoke would I need?
Thanks alot everyone! i plan to order this soon so it would be very helpful

12-15-10, 01:15 PM
Denny's will give you a sheet you fill out with all the specs and measurements. It is on their website.

Just use your stock shaft until you get your engine installed and running ;)

12-17-14, 10:13 PM
hey i just put a 1995 impala ss axle in my 1970 cadillac. the axles are the same in the 94 to 96 impala ss's. its a little less than an inch narrower than the caddy rear end. you can weld to the case which is a total plus. it comes with matching bolt pattern (though different thread count) disc brakes and a posi to boot. its a gm 8.5 inch rear so i now have access to a universe of aftermarket products. as far as sitting lower ive had no problems with the rake or anything of the like, though i did have to fork over a extra 400 for a custom drive shaft. im now running 4.11 gears and a tru trak limited slip and couldnt be happier. except n long drives which this car isnt really great for these days (cost of fuel) anyway. everything said and done zero to rebuilt impala ss gm 8.5 rear installed and running im under 2000. including all new bearings gaskets gear set rotors pads calipers lines parking brake cables it came with the true track limited slip which was like finding gold but we all get lucky sometimes

12-17-14, 10:29 PM
You can swap out the M12x1.5 lugs in that SS rear to match the ones on your front rotors without even taking the axles out.

12-18-14, 12:34 AM
Never even thought of that Jay, I'm gonna have to check it out next time I'm at the parts store. I've always worried that somebody will be helping me swap the rims or something and mix the lugnuts up.

Hey shadow, you still have the th400 in? What is cruising rpm at 60? Any vibration from the custom driveshaft? I got a th400, impala rear and a custom driveshaft but have a harmonic vibration at highway speeds. Maybe it's the axle bearings or a bent axle.

12-20-14, 12:52 AM
yes still got the th400, its out at my friends shop getting rebuilt with more clutches and a deeper aluminum oil pan and some other goodies. but as i recall at highway speed i was doing about 3500 in the right lane around 55-60 mph-ish. hard to tell i still had the original speedo gears so it was telling me i was doing 80mph when i was really doing like 45mph. no vibrations at highway speed. if you punch it on the highway it would have no problem getting into the 6000 and up rpm range which i have to be mindful to keep from doing because of my stock rocker arms and how they tend to fall apart at rpms in excess of 5000. but ill change them soon too. the rest of my engine rebuild can do the higher rpms.

12-20-14, 05:10 PM
Nice. You mind want to try calling rocker arm specialist. When I called and got parts for another rocker setup, they bought my stock rocker setup from me. I think they make a shaft system out of the stock rockers and pedestals but I didn't ask what they needed them for.